Photomask pattern correcting method and photomask corrected by the same and photomask pattern correcting device

ABSTRACT

A plurality of photomask pattern data are received at a time so as to carry out, with respect to an entire region of each photomask, correction for the optical proximity effect in a photoresist. Also, from the entire region of each photomask, an underlayer correction range which requires being corrected with respect to the optical proximity effect due to a base structure of the photoresist is automatically extracted so as to correct the photoresist within only the underlayer correction range. Further, from the entire region of each photomask, a development correction range which requires being corrected with respect to receding of edges and pattern deformation of the photoresist generated during development is automatically extracted so as to correct the photoresist within only the development correction range with respect to the development of the photoresist. As a result, it is possible to accurately and rapidly correct a photomask pattern for forming of a photoresist pattern.

This is a divisional of application Ser. No. 09/046,564, filed Mar. 24,1998, now U.S. Pat. No. 6,137,901 the entire content of which is herebyincorporated by reference in this application.

FIELD OF THE INVENTION

The present invention relates to a photomask pattern correcting methodfor correcting a pattern of a photomask used when exposing in alithography process which is one of the manufacturing processes of asemiconductor device, and to a photomask corrected by the same, and to aphotomask pattern correcting device.

BACKGROUND OF THE INVENTION

In a lithography process, which is one of the manufacturing processes ofa semiconductor device, various types of light energies such as visiblelight, UV light, or electron beam are projected on a target for exposureso as to transfer a desired pattern thereon.

In recent years, more refined and highly integrated semiconductorelements have been developed. In response to this, in the lithographytechnique, in order to achieve a minimum processing dimension of notmore than 0.1 μm, a super resolution lithography technique capable ofprocessing with a dimension substantially the same as or less than thewavelength of the exposing light has been developed for practical use.

The practical limit of a resolution of pattern exposure is determined byvarious factors. Of those factors, in response to refining of patternsin recent years, the optical proximity effect has been one of the mainfactors determining the resolution limit. The proximity effect refers toa problem which is caused by the interference effect of a radiationenergy such as light between proximate patterns. Such a problem includesdeformation of a transfer pattern caused by interference within a singlepattern.

In the conventional lithography process, since the size of a transferpattern is sufficiently large compared with the wavelength of exposinglight, the problem of proximity effect is not caused. In the superresolution lithography technique, however, the proximity effectphenomenon is a big problem.

When the size of a transfer pattern is substantially the same as or lessthan the wavelength of exposing light, due to the proximity effectphenomenon and receding of edges (especially at line end) and a patterndeformation phenomenon of a photoresist during development, a differencein line-width and shape is generated between a pattern of a photomaskand a pattern transferred onto the photoresist.

For this reason, in the super resolution photolithography, in order toform a photoresist having a desirable pattern, it is one of the mostimportant techniques to accurately estimate the degree of deformationdue to the optical proximity effect, etc., generated when transferring,and to correct a photomask pattern. The same can be said for thelithography technique adopting an electron beam which has a largeinteraction, or other types of light energies.

To present, various attempts have been made to correct a photomaskpattern by accurately estimating the optical proximity effect. Forexample, Japanese Unexamined Patent publication No. 189913/1990(Tokukaihei 2-189913) discloses a method of correcting a photomaskpattern with respect to the optical proximity effect.

In the above publication, an improvement is made at a semiconductorelement level; however, in practice, correction at a chip level, i.e., alarge area of approximately several tens of millimeters square isrequired.

An example of correction with respect to the optical proximity effect ata chip level or at a block level is suggested in the followingpublication: S. Miyama, K. Yamamoto, et al., “Large area opticalproximity correction with a combination of rule-based andsimulation-based methods”, Jpn. J. Appl. Phys. Vol. 35 (1996/12) pp.6370-6373.

The following describes the correction steps with respect to theproximity effect carried out in the above conventional example referringto the flowchart of FIG. 13, and FIG. 14 and FIG. 15.

First, a distribution of light intensity in a projected image isdetermined from a pattern 30 of the photomask shown in FIG. 14, and acritical edge (transparent pattern edge or opaque pattern edge ofpattern 30) subject to correction with respect to the optical proximityeffect is extracted (S41 and S42). In FIG. 14, the hatched portionsindicate opaque portions, and the other portions indicate transparentportions (translucent portions) . Also, in FIG. 14, the critical edge isindicated by the heavy broken line E.

Then, an appropriate point for determining a correction amount of thecritical edge E is set as a correction point, and a 1D (one dimensional)context of the correction point is determined (S43). Namely, a binaryjudgement is performed with respect to a correction point on the arrow Cof FIG. 14 (for example, correction point P indicated by × in FIG. 14)so as to determine the 1D context which is bit map data representing thetransparent portion and the opaque portion indicated by “0” and “1”,respectively.

Thereafter, it is judged in S44 whether the 1D context thus determinedcoincides with any one of 1D contexts prepared beforehand in acorrection table of FIG. 15. If it is judged in S44 that the 1D contextscoincide, the correction amount is determined referring to thecorrection table so as to correct portions of the photomask patternrequiring correction to the correction amount thus determined (S47).Note that, the broken line in FIG. 15 indicates the correction point P.

On the other hand, in the case where the determined 1D context does notcoincide with any of the 1D contexts in the correction table, acorrection amount appropriate for the determined 1D context iscalculated by simulation (S45), and the determined 1D context and thecorrection amount determined in S45 are added to the correction table soas to update the correction table (S46). Then, the correction point isreplaced with another correction point appropriate for determining thecorrection amount for the critical edge E (S43), and a correction amountis determined referring to the updated correction table so as tocorrect, in the same way as above, portions of the photomask patternrequiring correction to the correction amount thus determined (S47).

The sequence of S43 through S47 is repeated until correction is finishedwith respect to all the correction points of the edge extracted in S42(S48), and when correction is finished with respect to all thecorrection points, the process is finished.

However, in the photomask pattern correcting method of the describedconventional example, contrast and gradient of light intensity aredetermined from a distribution of light intensity in a projected image,and a critical edge is determined with respect to target patterndimensions so as to carry out correction with respect to the opticalproximity effect in the photoresist.

That is to say, in the photomask pattern correcting method of theconventional example, it is impossible to carry out, along with thecorrection with respect to the optical proximity effect, correction withrespect to photoresist development and a difference in underlayer levelby extracting a critical pattern range associated with receding of edgesand pattern deformation of the photoresist generated during development,and line-width shifting, etc., of the photoresist due to the differencein underlayer level.

As a result, the photoresist pattern deviates from a desired pattern dueto the receding of edges and pattern deformation of the photoresist, orthe line-width shifting. In other words, the photomask patterncorrecting method of the conventional example has a problem in thataccurate correction cannot be carried out.

Further, in the photomask pattern correcting method of the conventionalexample, it is required that (1) simulation of a projected light opticalimage, (2) a calculation by simulation of photoresist exposure anddevelopment, and (3) a preparation of a correction table are carried outwith respect to all regions requiring correction. As a result, a largeamount of measurement data are required to be prepared in advance and anextremely long time is required for calculation, preventing fastcorrection from being carried out.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a photomask patterncorrecting method and a photomask pattern correcting device respectivelycapable of carrying out accurate and fast correction with respect to aphotomask pattern, and a photomask corrected by the-same.

In order to achieve the above-mentioned object, a photomask patterncorrecting method in accordance with the present invention for forming adesired photoresist pattern on a wafer by developing a photoresist afterexposure through a photomask includes the steps of (1) receiving, at atime, pattern data representing patterns of a plurality of photomasks,(2) automatically extracting, from an entire region of each of theplurality of photomasks on the pattern data, a development correctionrange which requires being corrected with respect to receding edges(especially at line end) and pattern deformation of a photoresistgenerated during development, (3) correcting, with respect todevelopment of the photoresist, the photoresist within only thedevelopment correction range, (4) automatically extracting, from theentire region of each of the plurality of photomasks on the patterndata, an underlayer correction range which requires being corrected withrespect to an optical proximity effect due to a base structure of thephotoresist, and (5) correcting, with respect to the base structure ofthe photoresist, the photoresist within only the underlayer correctionrange.

In the described method, correction is carried out with respect tophotoresist development, along with correction with respect to a basestructure of a photoresist. Thus, it is possible to accurately correct aphotomask pattern with respect to both of (i) receding edges (especiallyat line end) and a pattern deformation phenomenon of a photoresistdependent on a photoresist and pattern density, which occur duringdevelopment and (ii) the optical proximity effect due to an opticaldifference in underlayer level, which become problems in a pattern withprocessed dimensions not more than several times the wavelength ofexposing light.

Further, since correction is carried out after extracting a rangerequiring correction, correction of a photomask pattern can be carriedout efficiently, thereby realizing fast correction of a photomaskpattern.

Also, the described method includes an optical proximity effectcorrecting step which basically carries out correction with respect tothe optical proximity effect in a photoresist, thereby realizingaccurate photomask pattern correction for the optical proximity effectin a photoresist.

In order to achieve the afore-mentioned object, another photomaskpattern correcting method is provided in accordance with the presentinvention for forming a desired photoresist pattern on a wafer byexposing a photoresist by an exposing device through a photomask whichhas been made by a photomask drawing device. A region whose distancefrom an edge of the photomask is not more than a predetermined value isdesignated as an optical proximity effect effective range based on (1)an exposure wavelength, a numerical aperture, and a coherent factor ofthe exposing device and (2) a minimum feature size of the photomaskdrawing device so as to carry out correction with respect only to theoptical proximity effect effective range.

With this method, it is possible to effectively and accurately correct apattern shift of a photomask pattern, which becomes a problem inpatterning of a fine photomask, caused physically and chemically by aphenomenon such as an edge receding phenomenon during photoresistdevelopment which is dependent on an optical proximity effect andpattern density, thus making it easier to automate the photomask patterncorrection technique including the correction of the optical proximityeffect.

In the above methods, it is preferable to determine a transparentpattern density in the optical proximity effect effective range, and tocarry out correction for a pattern size shift during photoresistdevelopment with respect only to a region whose transparent patterndensity is not less than a threshold value if the photoresist ispositive type.

In this manner, the transparent pattern density of a photomask used in acertain step of a semiconductor manufacturing process is determined inthe optical proximity effect effective range, and it is judged, based ona comparison between the transparent pattern density and the thresholdvalue whether to carry out correction with respect to the pattern sizeshift during photoresist development. Next, correction with respect tothe pattern size shift during photoresist development is carried outwith respect only to a region whose transparent pattern density exceedsthe threshold value. As a result, it is possible to more efficientlycarry out the photomask pattern correction, and reduce the processingtime.

Incidentally, when the γ value is large, development is carried out withan amount of light which exceeds a certain amount; thus, the shape ofthe photoresist after development is determined substantially with thethreshold value of light intensity. On the other hand, when the γ valueis small, the shape of the photoresist after development becomesdependent on the exposure amount and the slope (distribution) of theexposure amount, and a pattern shift is generated. Thus, as the γ valuebecomes smaller, occurrence of pattern shift during photoresistdevelopment is increased.

In order to overcome this problem, in the above methods, it ispreferable to determine the region in which correction with respect tothe pattern shift during photoresist development should be carried outbased on the threshold value which is determined from the γ valuerepresenting the exposure sensitivity of the photoresist. As a result,it is possible to efficiently and accurately correct the photomaskpattern regardless of the exposure sensitivity of the photoresist.

Note that, in the above methods, the predetermined value is determinedby (aλ/NA)+δ, “a” being a positive coefficient which is determined inaccordance with the coherent factor of an exposing device, λ being theexposure wavelength of the exposing device, NA being the numericalaperture of the exposing device, and δ being the minimum feature size ofa photomask drawing device.

In order to achieve the afore-mentioned object, a photomask inaccordance with the present invention is pattern-corrected by any one ofthe described pattern correcting methods.

With the described methods, it is possible to provide a photomask whichallows a desirable photoresist pattern to be formed on a wafer even whena pattern shift dependent on the optical proximity effect and a patterndensity, such as an edge receding phenomenon, is generated duringphotoresist development.

In order to achieve the afore-mentioned object, a photomask patterncorrecting device for forming a desired photoresist pattern on a waferby developing a photoresist after exposure through a photomask includes(a) a pattern data input section for receiving, at a time, pattern datarepresenting patterns of a plurality of photomasks, (b) a developmentcorrection range extracting section for automatically extracting, froman entire region of each of the plurality of photomasks on the patterndata, a development correction range which requires being corrected withrespect to receding edges (especially at line end) and patterndeformation of a photoresist generated during development, (c) adevelopment correcting section for correcting, with respect todevelopment of the photoresist, the photoresist within only thedevelopment correction range, (d) an underlayer correction rangeextracting section for automatically extracting, from the entire regionof each of the plurality of photomasks on the pattern data, anunderlayer correction range which requires being corrected with respectto an optical proximity effect due to a base structure of thephotoresist, and (e) an underlayer correcting section for correcting,with respect to the base structure of the photoresist, the photoresistwithin only the underlayer correction range.

In the described arrangement, correction is carried out with respect tophotoresist development, along with correction with respect to a basestructure of a photoresist. Thus, it is possible to accurately correct aphotomask pattern with respect to both of (i) receding edges and apattern deformation phenomenon of a photoresist dependent on aphotoresist and pattern density, which occur during development and (ii)the optical proximity effect due to an optical difference in underlayerlevel, which become problems in a pattern with processed dimensions notmore than several times the wavelength of exposing light.

Further, since correction is carried out after extracting a rangerequiring correction, correction of a photomask pattern can be carriedout efficiently, thereby realizing fast correction of a photomaskpattern.

Also, the described arrangement includes an optical proximity effectcorrecting section which basically carries out correction with respectto the optical proximity effect in a photoresist, thereby realizingaccurate photomask pattern correction for the optical proximity effectin a photoresist.

For a fuller understanding of the nature and advantages of theinvention, reference should be made to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart showing one example of a photomask patterncorrecting method in accordance with the present invention.

FIG. 2 is a flowchart showing a method of development correction in thephotomask pattern correcting method of FIG. 1.

FIG. 3 is a flowchart showing a method of difference in underlayer levelcorrection in the photomask pattern correcting method of FIG. 1.

FIG. 4 is a block diagram showing one example of a photomask correctiondevice in accordance with the present invention.

FIG. 5 is a drawing showing a photomask pattern corresponding to atarget photoresist pattern.

FIG. 6 is a drawing showing how a photomask is divided into meshregions.

FIG. 7 is a drawing showing development correction ranges of thephotomask of FIG. 5.

FIG. 8(a) and FIG. 8(b) are explanatory drawings respectively showing aproximity effect effective range due to a difference in underlayer levelof a photoresist, and FIG. 8(a) and FIG. 8(b) are a cross sectional viewand a plan view thereof, respectively.

FIG. 9 is an explanatory drawing showing one example of a data base forline-width correction with respect to a difference in underlayer level.

FIG. 10 is a drawing showing one example of a photomask pattern whichhas been corrected by the photomask pattern correcting method of thepresent invention.

FIG. 11 is a drawing showing one example of a photomask pattern whichhas been corrected in accordance only with a projected optical image.

FIG. 12 is a drawing showing a photoresist prepared by using a photomaskhaving the pattern of FIG. 10.

FIG. 13 is a flowchart showing a conventional photomask patterncorrecting method.

FIG. 14 is an explanatory drawing explaining the conventional photomaskpattern correcting method.

FIG. 15 is a drawing showing a correction table used in the conventionalpattern correction method.

FIG. 16 is a flowchart showing another photomask pattern correctingmethod in accordance with the present invention.

FIG. 17 is a plan view showing a photomask pattern of gate electrodes ofan SRAM cell.

FIG. 18 is a graph showing a sensitivity (exposure amount dependency)characteristic curve of a positive photoresist.

FIG. 19 is a plan view showing a photomask pattern which has beencorrected by the photomask pattern correcting method in accordance withthe present invention.

FIG. 20 is a graph of a radius of an optical proximity effectcalculation range versus correction accuracy and calculation time, inthe method of a second embodiment and a conventional method.

FIG. 21 is a flowchart showing yet another photomask pattern correctingmethod in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[First Embodiment]

The following will describe one embodiment of the present inventionreferring to FIG. 1 through FIG. 13.

Note that, in this specification, correction with respect to receding ofedges and pattern deformation of a photoresist during developmentthereof will be referred to as photoresist edge development correction,or simply as development correction. Also, correction with respect tothe optical proximity effect due to an optical difference in underlayerlevel (for example, aluminum wiring) on an underlayer of the photoresistwill be referred to as difference in underlayer level correction. Also,correction with respect to the optical proximity effect between patternsor within a pattern of a single photoresist will be referred to simplyas optical proximity effect correction.

First, the following describes a photomask pattern correcting device inaccordance with the present invention. As shown in FIG. 4, a patterncorrection device 1 of the present invention is provided with a patterndata input section 2, a pattern data density calculating section 3, adevelopment correction range extracting section 4, a developmentcorrecting section 5, a difference in underlayer level checking section6, a difference in underlayer level correction range extracting section(underlayer correction range extracting section) 7, a difference inunderlayer level correcting section 8, an optical proximity effectcorrecting section 9, and an error judging section 10.

The following describes a photomask pattern correcting method inaccordance with the present invention referring to the flowcharts ofFIG. 1 through FIG. 3.

In the photomask pattern correcting method of the present invention,first, all the photomask pattern data (layout data) used in amanufacturing process of a semiconductor device are inputted to thepattern data input section 2 of the pattern correction device 1 (S1).

The pattern data represent a layout of a photomask pattern correspondingto a target photoresist pattern. The pattern data also represent apattern at a chip level or a block level. Also, the pattern data includedata of a structure of LSI (Large Scale Integrated Circuit) which is anunderlayer of the photoresist, for example, data of an underlayerstructure indicating the material, etc.

Secondly, the pattern data inputted to the pattern data input section 2is sent to the optical proximity effect correcting section 9. Theoptical proximity effect correcting section 9, upon receiving thepattern data, carries out correction of the optical proximity effect inthe photoresist with respect to the pattern data (S2), and outputs thepattern data thus corrected to the difference in underlayer levelchecking section 6 and the difference in underlayer level correctionrange extracting section 7.

Thirdly, the difference in underlayer level checking section 6 checks(a) a base structure (laminated structure) of the photoresist inaccordance with data of a base structure included in the inputtedpattern data and (b) presence or absence of an optical difference inunderlayer level (hereinafter simply referred to as difference inunderlayer level) with respect to each photoresist (S3) . Namely, dataof a layer underlying the photoresist being formed by the currentphotomask, i.e., data of the structure of the underlayer of thephotoresist are extracted geometrically, and it is judged whether adifference in underlayer level which causes line-width shifting of thephotoresist as shown by the arrows S of FIG. 8(a) and FIG. 8(b) ispresent. For example, in the case where the underlayer of thephotoresist is made of a material having high reflectance such asaluminum, it is judged that a difference in underlayer level is present.

Note that, FIG. 8(a) and FIG. 8(b) respectively show exposed portions 12a and non-exposed portions 12 b of a positive photoresist 12 when thepositive photoresist 12 having a thickness of 1.0 μm formed on anoxidation film 14 and an aluminum wire 13 having a thickness of 0.2 μmis exposed through (1) a photomask 11 composed of Cr opaque sections 11a and translucent sections 11 b and (2) an air layer 15.

In FIG. 8(a) and FIG. 8(b), the width of each of the Cr opaque sections11 a is the same, and the width of the non-exposed portion 12 b on thefar side of the aluminum wire 13 is 0.35 μm. On the other hand, thethickness of the non-exposed portion 12 b on the near side of thealuminum wire 13 is shifted from 0.35 μm to 0.30 μm due to the effect ofthe aluminum wire 13. That is to say, in this case, the line-widthshifting of 0.05 μm is caused by the aluminum wire 13.

Fourthly, if it is judged by the difference in underlayer level checkingsection 6 that the difference in underlayer level is present, thedifference in underlayer level correction range extracting section 7, inaccordance with the result of the judgement, extracts, as a rangerequiring the difference in underlayer level correction, a proximityeffect effective range due to the difference in underlayer level, fromthe entire region of each photomask in the pattern data (S4). On theother hand, if it is judged by the difference in underlayer levelchecking section 6 that the difference in underlayer level is absent,the difference in underlayer level correction range extracting section 7directly sends the pattern data to the pattern data density calculatingsection 3 and the development correction range extracting section 4without carrying out the difference in underlayer level correction.

The proximity effect effective range due to step-difference isdetermined to be a range whose distance from the optical step-differenceis not more than a predetermined value, for example, a range whosehorizontal: pattern distance from the optical difference in underlayerlevel is not more than 2λ/NA. In the arrangement of FIG. 8(a) and FIG.8(b), the position pointed by the arrow S in FIG. 8(a) is where theproximity effect due to step-difference is maximum, and the rangeindicated by the broken line B in FIG. 8(a) and FIG. 8(b) is where theproximity effect due to step-difference is prominent.

Fifthly, the difference in underlayer level correcting section 8, byrule or simulation, determines a correction amount (shift amount) ofphotomask dimensions in the proximity effect effective range due to aproximate step-difference, in accordance with difference in underlayerlevel data in the vicinity which have been prepared beforehand. Thedifference in underlayer level correcting section 8 then carries outdifference in underlayer level correction with respect only to theproximity effect effective range to the correction amount thusdetermined (S5), and sends the processed pattern data to the patterndata density calculating section 3 and the development correction rangeextracting section 4.

In the difference in underlayer level correction, distortion in thepattern shape is fed back to the pattern data of the photomask for thecorrection. The distortion in the pattern shape generated as a ray oflight is projected differently, due to the difference in underlayerlevel, on the edge of the photoresist pattern in a vicinity of adifference in underlayer level and a portion of the photoresist patternwhere there is no difference in underlayer level.

For example, the difference in underlayer level correction is carriedout in the following manner. The optical proximity effect of a layer(underlayer, mainly) different from the current layer is estimated inadvance, and a data base (table) representing a relation between (1)data indicative of patterns and (2) the correction amount for adifference in underlayer level is prepared. FIG. 9 shows one example ofthe contents of such a data base.

In FIG. 9, the strings of zeros and ones on the left side are datarepresenting ranges requiring the difference in underlayer levelcorrection. In each string, “0” indicates a position on the X-Ycoordinates not requiring the difference in underlayer level correction,and “1” indicates a position on the X-Y coordinates requiring thedifference in underlayer level correction. Also, in FIG. 9, thenumerical values (0.05) on the right side indicate a line-width shiftamount (unit is μm).

In the difference in underlayer level correction, first, it is judged inS31 whether the pattern data of each photomask are entered (as one ofthe items of an entry) in the data base. If it is judged in,S31 that thepattern data are in the data base, the difference in underlayer levelcorrection is carried out in accordance with the data base (S32). On theother hand, if it is judged in S31 that the pattern data are not in thedata base, the difference in underlayer level correction based onexposure simulation is carried out considering the difference inunderlayer level (S33), and in S34, the data base is updated inaccordance with the result of the simulation (S34).

Then, the pattern density calculating section 3 divides each transparentpattern (or opaque pattern) of the entire region of each photomask (eachlayer) in the inputted pattern data into a large number of mesh regionsof rectangular or triangular shapes, and one of the mesh regions isselected (S6), and in S7, the density of transparent patterns (or opaquepatterns) around the mesh region thus selected is calculated.

It is preferable that the mesh region has an area of not more than(kλ/4NA)². Here, k is a parameter which is set to, for example, 0.5 to0.7 in a certain process. λ is a wavelength of exposing light, and NArepresents the value of numerical aperture which is, for example, 0.5 to0.6 in a certain semiconductor device.

In the case of forming a target pattern 20 of gate-polysilicon of anSRAM (Static Random Access Memory) having a line-width of 0.25 μm in ashape shown in FIG. 5 (in the case of removing the photoresist of theopaque portion), it is required to irradiate the target pattern 20 ofthe photoresist. Thus, in this case, the pattern density calculatingsection 3 divides a transparent pattern 20 of the photomask into squaremesh regions, each of which is 0.0625 by 0.0625 μm square. Note that,FIG. 5 is a drawing showing the transparent pattern 20 of a photomask,before being subjected to correction, corresponding to the targetpattern 20 of the photoresist.

In the pattern density calculating section 3, the calculation oftransparent pattern density Eenv of the transparent mesh regions iscarried out by Equation (1), $\begin{matrix}{{Eenv} = {{Ds}{\sum{\Omega \quad \frac{{i\left( {x^{*},y^{*}} \right)}{\Delta \left( {x,y} \right)}}{r\left( {{x - x^{*}},{y - y^{*}}} \right)}}}}} & (1)\end{matrix}$

In Equation (1), Ω represents a transparent pattern density calculationrange, i(x*, y*) represents the value of light intensity on an arbitrarymesh region (x*, y*) in the transparent pattern density calculationrange Ω, Ds represents the total amount of exposure on the transparentpattern density calculation range Ω, Δ(x, y) represents the area of thetransparent mesh region (x, y), and r(x-x*, y-y*) represents a distancebetween the transparent mesh region (x, y) and the mesh region (x*, y*).Also, the transparent pattern density calculation range Ω is set to arange within a predetermined distance from the transparent mesh region(x, y).

Note that, although it is also possible to use Equation (2) instead ofEquation (1) to determine the transparent pattern density Eenv of thetransparent mesh regions, Equation (1) is preferable.

Eenv=DsΣΩi(x*,y*)Δ(x,y)Erf(x-x*, y-y*)  (2)

In Equation (2), Ω represents a transparent pattern density calculationrange, i(x*, y*) represents the value of light intensity on an arbitrarymesh region (x*, y*) in the transparent pattern density calculationrange Ω obtained from the simulation result of a projected opticalimage, Ds represents the total amount of exposure on the transparentpattern density calculation range Ω, and Δ(x, y) represents the area ofthe transparent mesh region (x, y). In Equation (2), Erf (x-x*, y-y*) isan error function which is represented by Equation (3). $\begin{matrix}{{{Erf}\left( {{x - x^{*}},{y - y^{*}}} \right)} = {{{Erf}(r)} = {\int_{r}^{\infty}{^{- \quad t^{2}}{t}}}}} & (3)\end{matrix}$

In Equation (3), r is a distance between the transparent mesh region (x,y) and the mesh region (x*, y*), which is represented by Equation (4).

r={square root over ((x-x*)²+L +(y-y*)²+L )}  (4)

The transparent pattern density Eenv of the transparent mesh regioncalculated in the pattern density calculating section 3 is inputted,together with the pattern data, to the development correction rangeextracting section 4. The development correction range extractingsection 4 compares in S8 (a) the transparent pattern density Eenv with(b) the threshold value a which is dependent on a sensitivitycharacteristic obtained from resist exposure and which has been setbeforehand, and it is judged in S9 whether the result of the comparisonsatisfies Equation (5).

Eenv≧α  (5)

Note that, the threshold value a is not given a specific value, but isset to an appropriate value in accordance with the photomask pattern,the exposure sensitivity characteristic of the photoresist, orprocessing itself. In practice, the threshold value a is changedstepwise so as to adjust the determination level for receding ofphotoresist edges and pattern deformation which occur duringdevelopment.

In the case where the transparent pattern density Eenv of thetransparent mesh region satisfies Equation (5), the developmentcorrection range extracting section 4 judges that the transparent meshregion is a development correction range requiring photoresist edgedevelopment correction, and inputs the transparent mesh region to thedevelopment correcting section 5.

A region which requires the photoresist edge development correctionincludes edges and corners of a line (opaque portion), edges of a space(translucent portion), and a contact, etc., in a single layer. In thepositive photoresist, regions on line edges whose Eenv is not less thanthe threshold value α, for example, edges of a pattern, are judged as adevelopment correction range, because such regions have high exposuredensity due to the pattern, and the amount of line-width shifting duringdevelopment is prominent in such regions.

For example, in the target pattern 20 of FIG. 5 (in the case of keepingthe exposed portions of the photoresist from being removed), L-shapedlong side edges 20 a of the gate-polysilicon, which are enclosed by thebroken circles in FIG. 7 are judged as a development correction range.

Then, in the development correcting section 5, the transparent meshregion is subjected to the photoresist edge development correction usinga data base (template) obtained from simulation or measured value of thephotoresist exposure and development (S10). Thereafter, the transparentmesh region is changed to a corrected transparent mesh region in S6, andthe sequence returns to S7.

Specifically, the photoresist edge development correction is carriedout, for example, in the manner shown in FIG. 2. Namely, a data baserepresenting a relation between the pattern and an optimum correctionamount is prepared beforehand from simulation or measured value of thephotoresist exposure and development.

In the photoresist edge development correction, first, it is judged inS21 whether the pattern data of each photomask are in the data base. Ifit is judged in S21 that the pattern data are in the data base, thedevelopment correction is carried out in S22 referring to the data base.On the other hand, if it is judged in S21 that the pattern data are notin the data base, the development correction is carried out in S23 basedon simulation, and in S24, the data base is updated in accordance withthe result of the simulation. Here, in order to add data to the database, not only the intensity of light but the simulation result ormeasured data of the photoresist exposure and development is required.

On the other hand, in the case where the transparent pattern densityEenv of the transparent mesh region does not satisfy Equation (5), thedevelopment correction range extracting section 4 judges that thetransparent mesh region does not require the photoresist edgedevelopment correction, and sends the pattern data to the error judgingsection 10, and also changes the transparent mesh region to a correctedtransparent mesh region in S6, and the sequence returns to S7.

The sequence of S6 to S10 is repeated until all the transparent meshregions are processed (S11), and the processed pattern data are sent tothe error judging section 10.

In the described manner, in the development correction range extractingsection 4, a range requiring the photoresist edge development correctionin accordance with the transparent pattern density is extracted, and thephotoresist edge development correction is carried out with respect onlyto the development correction range.

The error judging section 10 judges whether the difference between theinputted pattern data and the simulation result is below a predeterminedvalue, for example, five per cent (S12), and if the difference is belowthe predetermined value, the error judging section 10 outputs thecorrected pattern data, and the correction is finished. On the otherhand, if the difference is less than the predetermined value, the errorjudging section 10 sends the pattern data again to the optical proximityeffect correcting section 9, and the sequence returns to S2. After thesequence of S2 to S11 is repeated until the difference is below thepredetermined value, the corrected pattern data are outputted, and thecorrection is finished.

In the case where the pattern data representing the pattern of FIG. 7 iscorrected in the pattern correction device 1, the transparent pattern ofthe outputted pattern data (result of correction) takes a shape of, forexample, a pattern 21 as indicated by the solid lines of FIG. 10. Also,for comparison, a pattern 22, which is an example of a corrected pattern(result of correction) obtained only from the projected optical image,is indicated by the solid lines in FIG. 11. Note that, in FIG. 10 andFIG. 11, the hatched portions respectively indicate transparent portionsof the photomask, and the broken lines respectively indicate theoriginal pattern 20 shown in FIG. 20.

When the shape of a photoresist which was developed after exposure usingthe photomask of the pattern 21 of FIG. 10 was measured, a pattern 23 asindicated by the solid lines in FIG. 12 was observed. Note that, in FIG.12, the broken lines indicates the original pattern 20 of FIG. 7.

As described, in the photomask pattern correcting method of the presentinvention, it is possible to efficiently and rapidly correct a photomaskpattern with respect to all of (1) the optical proximity effect in aphotoresist, (2) receding edges and a pattern deformation phenomenon ofa photoresist dependent on pattern density and a resist sensitivitycharacteristic, which occur during development, and (3) the opticalproximity effect due to an optical difference in underlayer level, whichbecome problems in a pattern with processed dimensions not more thanseveral times the wavelength of exposing light.

Also, as described above, by extracting in advance a correction rangenot directly, but indirectly, associated with the proximity effect, itis possible to correct the optical proximity effect in a photomask at atime the line-width of the transparent portion of a photomask inaccordance with the value of a projected optical image (simulation) withrespect to all the regions. This is important in automatic correction ofa photomask pattern having a large area at a chip level or a blocklevel.

With the described arrangement, compared with a conventionalarrangement, the proximity effect correction can be significantlysimplified so as to allow the operation of photomask pattern correctionto be carried out efficiently and integrally. As a result, it ispossible to make the automation of the photomask pattern correctiontechnique including the correction of the optical proximity effecteasier, and to put the photomask pattern correction technique at a chiplevel into a practical application.

Note that, the photomask pattern correcting method and the photomaskpattern correcting device of the present invention are particularlysuitable for forming on a wafer, using a photomask, a fine photoresistpattern not more than several times a wavelength of exposing light byexposure and development.

[Second Embodiment]

The following will describe a second embodiment of the present inventionreferring to FIG. 16 through FIG. 20.

In the photomask pattern correcting method of the present embodiment,first, data of a layer to be subjected to correction is extracted fromdata of a plurality of layers included in layout data of a photomask,and a transparent (or opaque) pattern on the layer data is divided intomesh regions of a rectangle or triangle having an area of not more than(kλ/4NA)² so as to carry out a pattern correction on the photomask withrespect to each mesh region. It is preferable that the size of the meshregion be substantially (kλ/4NA)² since a mesh region which is too smallincreases the calculation steps.

Here, k is a parameter called a process constant which is determined bythe characteristics of the semiconductor device (exposing device), whichusually takes a value of 0.4 to 1.0. λ is an exposure wavelength of theexposing device, and NA is the numerical aperture of the exposingdevice.

In the method of First Embodiment, as shown in FIG. 6, the range ofcorrection calculation is not specified, and surrounding patterns(adjacent patterns) are divided into mesh regions so as to carry out acorrection calculation with respect to all the adjacent surroundingpatterns. In contrast, in the method of the present embodiment, thecorrection calculation is carried out with respect only to the opticalproximity effect effective range, but not to a distant pattern.

Namely, in the photomask pattern correction method in accordance withthe present embodiment, based on (1) an exposing wavelength λ, theexposing device, the numerical aperture NA, and a coherent factor σ,which are optical parameters, and (2) a minimum feature size δ of aphotomask drawing device, a region whose distance from the photomaskpattern edge is not more than a predetermined value Leff is designatedas the optical proximity effect effective range (region which isaffected greatly by the pattern deformation caused by optical proximityeffect) so as to carry out a pattern correction for optical proximityeffect. Namely, the optical proximity effect correction is carried outwith respect only to the optical proximity effect effective range, thusefficiently and accurately correcting the photomask pattern.

Also, the optical proximity effect correction is a correction of aphotomask pattern with respect to an exposing image (light intensitydistribution) when the photoresist is exposed through the photomaskpattern of the LSI. When exposing the photoresist in thephotolithography process, diffraction of light from the transparentportion becomes a problem. In the optical proximity effect correction,the photomask pattern is corrected so as to cancel the effect ofdiffracted light as much as possible.

The following describes specifically a method for determining the meshregion and the optical proximity effect effective range, using, as anexample, a KrF laser exposing device (exposing wavelength=248 nm).

First, the size Sm (μm) of a mesh region is determined in the followingmanner. Namely, when NA=0.35 and k=0.7, the size of a mesh region Sm isdetermined in the following manner:

Sm=kλ/4NA=0.7×0.248/(4×0.35)=0.124

Also, when NA=0.4 and k=0.7, the size of a mesh region Sm is determinedin the following manner:

Sm=kλ/4NA=0.7×0.248/(4×0.4)=0.108

The predetermined value Leff for determining the optical proximityeffect effective range is determined by:

(aλ/NA)+δ

where “a” is a positive coefficient which is determined in accordancewith the coherent factor of the exposing device, λ is the exposingwavelength of the exposing device, NA is the numerical aperture of theexposing device, and δ is the minimum feature size of the photomaskdrawing device.

More specifically, the predetermined value Leff is determined by thefollowing equations:

Leff (λ, NA, σ)=3{square root over (2λ)}/4NA+δ  (6)

when 0.1≦σ≦0.3;

Leff (λ, NA, σ)=3{square root over (2λ)}/3NA+σ′  (7)

when 0.3<σ<0.5; and

Leff (λ, NA, σ)=3{square root over (2λ)}/2NA+δ″  (8)

when 0.5≦σ

For example, when σ*=0.2, NA=0.4, δ=0.2 μm, and λ=0.248 μm, fromEquation (6), Leff=0.855.

Note that, an exposing device with σ of less than 0.1 is not taken intoconsideration since such a device does not exist at present, and isunlikely to be realized in the future. Also, in Equations (6) to (8),the optical aberration (spherical aberration) of the exposing device isnot considered because it is sufficiently smaller than Leff.

The factors 3{square root over (2/4)}, 3⅔, and 3{square root over (2/2)}of Equations (6) to (8), respectively, are determined from data ofactual measurement. Also, because the minimum feature size of thephotomask drawing device differs depending on the coherent factor(positioning accuracy) σ, the coherent factors δ, δ′, and δ″ ofEquations (6) to (8) have different values, respectively.

The following describes, as a specific example of the optical proximityeffect effective range, the optical proximity effect effective range ofa photomask pattern of gate electrodes of SRAM (Static Random AccessMemory).

Here, assuming that the target mesh region is the region shown in FIG.17, the estimation for the optical proximity effect effective range withrespect to a mesh region A of the pattern edge in this region is carriedout in the optical proximity effect effective range as enclosed by thebroken circle line in FIG. 17. The optical proximity effect effectiverange is determined as a range having a radius Leff where the center ofthe range is the mesh region A on the photomask.

Incidentally, as shown in FIG. 18, in a photoresist whose slope γ (slopeat the middle of the inclined portion of the sensitivity characteristiccurve) representing the exposure amount dependency (photosensitivitycharacteristic) is steep, the pattern dependency is low. Thus, in such aphotoresist, even when adversely affected by other patterns, a patternshift does not occur, and no problem is presented.

In contrast, in a photoresist having a relatively gradual slope γrepresenting the exposure amount dependency (photosensitivitycharacteristic), pattern dependency from surrounding patterns is high,and a pattern shift is easily generated during photoresist development.The photoresist starts being exposed with a certain amount of light, andis removed during development when exposure amount is above a certainamount. However, when the slope γ is gradual, the photoresist is exposedwith only a small amount of light, and the film is reduced. When theexposing amount (energy) is small, the photoresist is not exposed sothat the photoresist remains without being developed.

Note that, in FIG. 18, d0 represents a film thickness of a positivephotoresist before development, and d represents a film thickness of apositive photoresist after development. Thus, the vertical axis in thegraph of FIG. 18 represents a film change in the vertical direction(change in film thickness) of the positive photoresist. Also, in FIG.18, the rotation speed during application of a photoresist is 3,000 rpm,and the film thickness of the positive photoresist after application ofthe photoresist is 10,205 Å. Further, although not shown in FIG. 18, onthe pattern edge of the positive photoresist, film reduction in thelateral direction, namely, a pattern shift is generated.

As described, since a photoresist whose y value is small is exposed by asmall amount of light, a problem is presented in that the pattern shiftduring development of photoresist becomes larger by more than theproximity effect. In order to overcome such a problem, when the patternshift during photoresist development is large, in addition to theoptical proximity effect correction, correction with respect to thepattern shift during photoresist development, namely, photoresistdevelopment correction is also carried out in the optical proximityeffect effective range. Note that, the photoresist developmentcorrection refers to correction for a photomask pattern with respect tothe shape of the photoresist after exposure and development.

In contrast, when the exposure amount dependency of the photoresist islarge, namely, when the γ value (slope at the middle of the inclinedportion of the sensitivity characteristic curve of the photoresist inFIG. 18) representing the sensitivity characteristic of the photoresistis not less than 10, since the threshold model of the exposing amount iswell-established, sufficient correction can be carried out only with theoptical proximity effect correction based on the optical image withoutconsidering the pattern shift during photoresist development. Thus, asshown in FIG. 18, when the exposure dependency of the photoresist issufficiently large, namely, when the slope γ is steep (large), it is notrequired to carry out photoresist development correction.

Also, in the case where the γ is gradual and less than 10, the patterndensity Eenv is calculated, and it is judged, based on the conditionEenv≧α, whether correction with respect to photoresist development isrequired. When the slope γ is steep, α becomes larger and Eenv<α, andcorrection with respect to photoresist development is not required.

Thus, with respect to a region of the pattern satisfying the conditionof Eenv≧α, both the optical proximity effect correction and developmentcorrection are carried out, and with respect to a region satisfying thecondition of Eenv<α, only the optical proximity effect correction iscarried out. Because the development correction is carried out withrespect only to the region which has been subjected to the opticalproximity effect correction, it is ensured that the region which issubjected to the development correction is also subjected to the opticalproximity effect correction. Thus, the optical proximity effect is takeninto consideration for the pattern shift after development.

The pattern density Eenv around the target mesh region is calculated,for example, by the following Equation (9) or (10): $\begin{matrix}{{{Eenv}\left( {x,y} \right)} = {{Ds}{\sum\limits_{\Omega}\frac{{i\left( {x^{*},y^{*}} \right)}{\Delta \left( {x,y} \right)}}{\left\lbrack {r\left( {{x - x^{*}},{y - y^{*}}} \right)} \right\rbrack^{2}}}}} & (9)\end{matrix}$

 Eenv(x,y)=DsΣ_(Ω) _(^(i)) (x*,y*)Δ(x,y)Erf (x-x*,y-y*)  (10)

Erf(x − x^(*), y − y^(*)) = ∫_(r)^(∞)^(−  t²)t

Where

r={square root over ((x-x*)²+L +(y-y*)²+L )}

Here, i(x*, y*) is a light intensity as specified by simulation of aprojected optical image, Ω denotes a region for which the patterndensity is calculated, Ds is the exposure amount of the region Ω, Δ(x,y) is an area of an arbitrary transparent portion, r(x-x*, y-y*) is adistance between mesh regions, and Erf denotes an error function.

Of the two Equations (9) and (10), the former is preferable becauseEquation (9) is more accurate and is more suitable for the presentoptical proximity effect than Equation (10) which employs the errorfunction which is used generally simply for a statistical purpose.

Incidentally, when the γ value is large, development is carried out withan amount of light which exceeds a certain amount; thus, the shape ofthe photoresist after development is determined substantially with thethreshold value of light intensity. On the other hand, when the γ valueis small, the shape of the photoresist after development becomesdependent on the exposure amount and the slope (distribution) of theexposure amount, and a pattern shift is generated. Thus, as the γ valuebecomes smaller, occurrence of pattern shift during photoresistdevelopment is increased.

Unlike the γ value and the pattern density Eenv which are determined bycalculation, the threshold value a is determined from experimental datain accordance with the γ value (γ value of the slope of the curve inFIG. 18) representing the exposure sensitivity of the photoresist.Namely, with respect to each processing condition (types of photoresist,baking temperature, developing time, etc.), the pattern density Eenv isvaried, and a minimum pattern density Eenv for which correction isrequired, as the pattern shift during development is made larger byreceding of line edges, is given the α value.

The following will describe in detail a photomask pattern correctionmethod in accordance with the present embodiment referring to theflowchart of FIG. 16.

First, photomask pattern data (for example, layout data) used in themanufacturing process on the semiconductor device are inputted into thepattern correction device with respect to data of each layer (S51).

Secondly, the photomask pattern data are sent to the optical proximityeffect correcting section of the pattern correction device. In theoptical proximity effect correcting section, the critical edge isextracted (S52). The critical edge is a region which requires patterncorrection, for example, a region requiring correction of a line-width(or space) as a result of a change in pattern density, and an edge of afine line or outer side of the corner where receding is expected forwhich supplement pattern such as serif is required. Serif is a bumpysupplement pattern provided so as to project from the corner of a dynepattern (opaque portion if the photoresist is positive type).

Thirdly, the extracted critical edge on the layout pattern is dividedusing the optical proximity effect effective range as a reference, and amesh region for calculation is set per optical proximity effecteffective range (S53).

Fourthly, with respect to one of the critical corners (critical edges)on the photomask pattern, a degree to which the corner is affected bysurrounding patterns is calculated in a region with a radius Leff, ofwhich the center is the critical corner. Also, in a region with a radiusLeff (optical proximity effect effective range), of which the center isanother corner or an adjacent mesh region (adjacent side or adjacentcorner), a degree to which the corner is affected by surroundingpatterns is calculated. In this manner, with respect to each criticalcorner on the photomask pattern, the effect of the surrounding patternsis calculated one after another. Also, in S53, calculation of Leff andsetting of the optical proximity effect effective range are carried outbefore or after setting the mesh region.

Fifthly, optical proximity effect correction calculation is carried out(S54). Namely, using the optical proximity effect effective range as areference, an optical image of the photomask pattern is calculated usingthe mesh region which has been set in S53, and pattern correction iscarried out in a region of which an error with respect to the targetpattern is large.

Note that, the optical image of the photomask pattern is an aerial imagein the case where the photoresist is not present, or a latent image inthe case where the photoresist is present considering the refractiveindex and absorptivity which are the properties of the photoresist.

Sixth, the sensitivity characteristic of the photoresist is judged(S55). Namely, based on the sensitivity characteristic of thephotoresist under predetermined photolithography processing conditions,exposure amount dependency of the photoresist is evaluated, and when theγ value is sufficiently large, not less than 10, the sequence goes toS59, and when the γ value is less than 10, the sequence goes to S56.

Seventh, with respect to a position where the optical proximity effectis to be evaluated, based on Equations (9) and (10), surrounding patterndensity is calculated in the optical proximity effect effective range.(S56).

Eighth, based on the surrounding pattern density obtained from thepattern density calculation, it is judged whether the developmentcorrection is required in the process (S57). For example, when theprocess is a positive photoresist process such as a positive chemicalamplified photoresist process, the development correction is carried outwith respect to a region with a pattern density Eenv of not less than apredetermined value α. On the other hand, when the pattern density Eenvis less than α, the sequence goes to S59. Note that, the chemicalamplified photoresist is a photoresist which generates acid uponexposure and reacts with the acid thus generated.

Ninth, pattern correction (photoresist development correction)considering the line-width shift amount during photoresist developmentis carried out (S58), and the sequence goes to S59.

Tenth, a correction finishing judgment is carried out (S59). Namely, itis judged whether correction has been carried out with respect to all ofthe critical portions in the pattern on the entire photomask, i.e., withrespect to all the extracted critical edges which have been extracted inS52. When there is a critical edge which has not been corrected, thesequence returns S54. When the sequence returns to S54 from S59, theoptical proximity effect correction in S54 is carried out by using thesame Leff which has been used in the previous round. Finally, patterncorrection is carried out with respect to all the critical edges whichhave been extracted in S52, and the process is finished.

By the described method, the photomask pattern is corrected, forexample, to the pattern shown in FIG. 19.

FIG. 20 shows the results of a comparison between the method of thepresent embodiment and the conventional method, which was made withrespect to the radius r (μm) of the optical proximity effect effectiverange (calculation range) during development against a change incorrection accuracy (calculation accuracy) and calculation time. FromFIG. 20, it can be seen that in the method of the present embodimentusing Leff, compared with the conventional method which does not useLeff, the calculation time is greatly reduced.

As described, in the photomask pattern correction method of the presentembodiment, the optical proximity effect effective range is set usingLeff, and the photomask pattern is corrected based on simulation andmeasured data, and the surrounding pattern density is calculated so asto extract a pattern shift region during development. This significantlyreduces the number of optical proximity effect correction steps whichhad been required conventionally, and allows the photomask patterncorrection to be carried out efficiently and accurately.

[Third Embodiment]

The following describes a third embodiment of the present inventionreferring to FIG. 21.

In the photomask pattern correction method in accordance with thepresent embodiment, as shown in FIG. 21, after pattern data have beeninputted in the same manner as in S51 of FIG. 16 (S61), a mesh region isset using Leff having a predetermined value with respect, not to theentire photomask, but to a region which is likely to present a problem(pattern edge or a region with a high density pattern) (S62).

Then, as in S54, correction is carried out using Leff having apredetermined value with respect to the optical proximity effect (S63).Also, as in S3, presence or absence of an underlayer level is judged(S64). When an underlayer level is not present, the sequence goes toS67. When an underlayer level is present, as in S4, the opticalproximity effect effective range is extracted as a range requiringcorrection due to the difference in underlayer level (S65), and aftercarrying out the underlayer level correction as in S5 (S66), thesequence goes to S67.

Since S67 to S71 are the same as S54 to S58, explanations thereof areomitted. After S67 to S71, as in S11, it is judged in S72 whethercorrection for all the mesh region has been finished. When it is judgedin S11 that the correction has been finished with respect to all themesh regions, as in S12, it is judged in S73 whether a differencebetween the simulation result and the target pattern is below apredetermined value. When the difference is not below the predeterminedvalue, the sequence returns to S63, and when the difference is below thepredetermined value, the correction is finished.

As described, in the photomask pattern correcting method in accordancewith the present embodiment, because the underlayer level correction iscarried out with respect to the proximity effect effective range inaddition to the method of second embodiment, it is possible to moreaccurately correct the pattern shift of the photomask pattern.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A method for correcting a pattern of a photomaskfor forming a desired photoresist pattern on a wafer by developing aphotoresist after exposure through a photomask, comprising the steps of:(1) receiving, at a time, pattern data representing patterns of aplurality of photomasks; (2) automatically extracting, from an entireregion of each of the plurality of photomasks on the pattern data, adevelopment correction range which require being corrected with respectto receding edges and pattern deformation of a photoresist generatedduring development; (3) correcting, with respect to development of thephotoresist, the photoresist within only the development correctionrange; (4) automatically extracting, from the entire region of each ofthe plurality of photomasks on the pattern data, an underlayercorrection range which require being corrected with respect to anoptical proximity effect due to a base structure of the photoresist; and(5) correcting, with respect to the base structure of the photoresist,the photoresist within only the underlayer correction range.
 2. Themethod as set forth in claim 1, further comprising the step of:correcting the optical proximity effect in the photoresist with respectto the entire region of each of the plurality of photomasks.
 3. Themethod as set forth in claim 1, wherein in said step (2), the entireregion of each photomask is divided into mesh regions on the patterndata of each photomask, a pattern density is determined for each of themesh regions and the development correction range is extracted inaccordance with the pattern density and a sensitivity characteristic ofthe photoresist.
 4. The method as set forth in claim 1, wherein in saidstep (2), presence or absence of an optical difference in underlayerlevel on a base of the photoresist is judged in accordance with basestructure data of the photoresist, and the underlayer correction rangeis extracted, in a case where a step-difference is present, inaccordance with a distance from the optical difference in underlayerlevel.
 5. The method as set forth in claim 1, wherein in said step (2),the entire region of each photomask is divided into mesh regions on thepattern data of each of the plurality of photomasks, a pattern densityis determined for each of the mesh regions, and the developmentcorrection range is extracted in accordance with a comparison of (a) thepattern density and (b) a threshold value dependant on a predeterminedsensitivity characteristic of the photoresist.
 6. The method as setforth in claim 1, further comprising the step of: judging whether adifference between (a) the pattern data subjected to the developmentcorrection and the underlayer correction and (b) a simulation result isnot more than a predetermined value, wherein in a case where thedifference exceeds the predetermined value, said step (3) and said step(5) are repeated again.
 7. A photomask pattern correcting device forforming a desired photoresist pattern on a wafer by developing aphotoresist after exposure through a photomask, comprising: a patterndata input section for receiving, at a time, pattern data representingpatterns of a plurality of photomasks; a development correction rangeextracting section for automatically extracting, from an entire regionof each of the plurality of photomasks on the pattern data, adevelopment correction range which require being corrected with respectto receding edges and pattern deformation of a photoresist generatedduring development; a development correcting section for correcting,with respect to development of the photoresist, the photoresist withinonly the development correction range; an underlayer correction rangeextracting section for automatically extracting, from the entire regionof each of the plurality of photomasks on the pattern data, anunderlayer correction range which require being corrected with respectto an optical proximity effect due to a base structure of thephotoresist; and an underlayer correcting section for correcting, withrespect to the base structure of the photoresist, the photoresist withinonly the underlayer correction range.
 8. The photomask patterncorrecting device as set forth in claim 7, further comprising: anoptical proximity effect correcting section for correcting the opticalproximity effect in the photoresist with respect to the entire region ofeach of the plurality of photomasks on the pattern data.
 9. Thephotomask pattern correcting device as set forth in claim 7, wherein insaid development correction range extracting section, the entire regionof each photomask is divided into mesh regions on the pattern data ofeach photomask, a pattern density is determined for each of the meshregions and the development correction range is extracted in accordancewith the pattern density and a sensitivity characteristic of thephotoresist.
 10. The photomask pattern correcting device as set forth inclaim 7, wherein in said underlayer correction range extracting section,presence or absence of an optical difference in underlayer level on abase of the photoresist is judged in accordance with base structure dataof the photoresist, and the underlayer correction range is extracted, ina case where a step-difference is present, in accordance with a distancefrom the optical difference in underlayer level.
 11. The photomaskpattern correcting device as set forth in claim 7, wherein in saiddevelopment correction range extracting section, each photomask isdivided into mesh regions, and the development correction range isextracted in accordance with a comparison of (a) the pattern density and(b) a threshold value dependant on a predetermined sensitivitycharacteristic of the photoresist.
 12. The photomask pattern correctingdevice as set forth in claim 7, further comprising: an error judgingsection for judging whether a difference between (a) the pattern datasubjected to the development correction and the underlayer correctionand (b) a simulation result is not more than a predetermined value so asto send, in a case where the difference exceeds the predetermined value,the corrected patten data to said development correcting section andsaid underlayer correcting section.